Offset cylinder and piston rod mounting for hydraulic dump bodies



March 15, 1955 J. M. GwlNN, JR 2,704,221

OFFSET CYLINDER AND PISTON ROD MOUNTING F OR HYDRAULIC DUMP BODIES FiledMay 27. 195o 2 sheets-sheet 1 March 15, 1955 J. M. GwlNN, JR 2,704,221

OFFSET CYLINDER AND PIsIoN ROD MOUNTING FOR HYDRAULIC DUMP BODIES FiledMay 27, 1950 2 Sheets-Sheet 2 IN V EN TOR.

United States Patent O OFFSET CYLINDER AND PISTON ROD MOUNTING FORHYDRAULIC DUMP BODIES Joseph M. Gwinn, Jr., Dearborn, Mich., assignor toGar Wood Industries, Inc., Wayne, Mich., a corporation of MichiganApplication May 27, 1950, Serial No. 164,761

7 Claims. (Cl. 298-22) This invention relates to hoists or elevatingmechanism of the type that may be employed in dump trucks, and, inparticular, refers to hoists that are empowered by pressure lluid such'as oil. One embodiment of the invention is disclosed in a copendingapplication, Serial No. 121,106, filed October 13, 1949, of the presentinventor entitled Arm and Tension Link Hoist.

In hoists of the type to which the present invention relates, liftingforce is ordinarily furnished by a hydraulic cylinder containing apiston with a rod that passes through a gland to extend outside of thecylinder. The cylinder 1s usually pivoted or otherwise connected to thechassis fr ame or sub-frame and the rod is usually pivoted, eitherdirectly or through linkage (such as shown in the aforementionedapplication), to the body that is to be elevated and lowered, though itis possible to reverse the arrangement. While the present invention isillustrated herein in connection with direct lift hoists wherein the rodis piv oted directly to the bottom of the body and the cylinder to theframe, it can also be used in hoists wherein the rod is connected to thebody and the cylinder to the frame through the intermediary of othermembers.

The invention centers about the locations of the connections between theframe and cylinder and between the rod and body. It resides,principally, in offsetting the axes of these connections, which areusually pivotal, from the axis of the piston rod and the pressurecylinder. The offset or eccentricity is preferably such that the line offorce through the rod pivot passes through the axis of the rod at apoint of intersection which lies between the piston and the gland whenthe rod is fully extended.

This construction has several functional advantages of which three willbe noted. First, it increases the moment arm of the force applied to thebody through the rod. In direct lift hoists, the moment arm is theperpendicular distance from the line through the two pivots to thebodyframe pivot. This distance is increased with the present inventionsince the offset of the rod-body pivot is upward and the offset of thecylinder frame pivot is downward. The aforementioned copendingapplication shows how the moment arm is increased in arm type hoists.The increase in moment arm enables the use of lower oil pressures orsmaller cylinders.

A second advantage lies in the fact that the construction eliminatescocking of the piston and rod axis with respect to the cylinder axis.When the line of force passes through the rod axis at an angle and at apoint between the piston and the gland, the side loads on the piston andgland are in the same direction so that the possibility of cooking orbinding is eliminated. Thus, the piston rod remains parallel with theaxis of the cylinder and good bearing contact is obtained between boththe piston and cylinder and the rod and gland to distribute the bearingloads. In conventional constructions, these loads tend to concentrate atthe corners of the piston and gland due to the angle assumed by the rodaxis relative to the cylinder axis.

A third advantage of the present construction resides in the eliminationof piston rod failures due to abnormal conditions and stresses which aredifficult to calculate. With ordinary constructions in which the pivotconnections of both the cylinder and rod lie on the cylinder and rodaxis, or in which only the cylinder base attachment to the frame isoffset below the axis, deflections of the assembly due to play or due toelastic deformation or to friction in the pivots increase the bendingload on the piston rod and the possible maximum bending stress under2,704,221 Patented Mar. 15, 1955 conditions of use is almost impossibleto estimate. In the construction of the present invention, the load onthe rod is oiset or eccentric by design and the maximum bending stressis readily calculated. Play does not increase the bending stress andfriction at the rod pivot actually reduces the bending stress due to theoiset load.

It should also be noted that though in most cases the rod will beconnected to the body and the cylinder base to the frame, the reversearrangement, if employed, may also embody the concepts of thisinvention. ln this case, both the cylinder base connection to the bodyand the rod connection to the frame will, in accordance with thepreferred practice of the invention, be offset and arranged so that theline of force intersects the rod axis between the piston and the gland.

The principles of the invention are more fully described and illustratedin connection with the accompanying drawings, wherein:

Figure l is a side elevation with parts broken away of a dump truckembodying hoist mechanism constructed in accordance with the invention;

Fig. 2 is a plan view, with parts broken away, of the construction shownin Fig. l when the body is elevated so that the pressure cylinder isvisible;

Fig. 3 is a vertical axial section through hydraulic elevating mechanismconstructed in accordance with the principles of the invention;

Fig. 4 is a vertical axial section through a modified forn of elevatingmechanism embodying the invention; an

Fig. 5 is a vertical axial section through conventional hydraulic hoistmechanism and illustrates cocking of the piston and rod in the cylinderand gland.

The dump truck 1 illustrated in Figs. 1 and 2 has a chassis 3 that issupported in a suitable manner upon wheels 5. The body' and itsoperating mechanism can be mounted directly on the chassis frame, ifdesired, but in the preferred construction illustrated, the body and itsoperating mechanism are mounted on an auxiliary subframe 6, and thusform a unit which may be installed on the chassis by bolting the twoframes together. The body 7 has longitudinal sills 8 on which aresecured downwardly extending legs or brackets 9 adjacent the rearthereof which are journaled by means of pins 11 in suitable bearings 13in the sub-frame 6. The body 7 is normally supported in a horizontalposition, and when dumping is desired. hoist mechanism 15 between thebody and the sub-frame 6 is actuated to pivot the body 7 upwardly aboutthe axis of pins 11.

The hoist mechanism 15 that is illustrated in Figs. l to 3 is of thedirect actuating type. Thus, it includes a pressure housing or cylinder17 that is pivoted at its base or forward end 19 to the sub-frame 6.This connection is accomplished through the medium of a pivot plate 21to which the cylinder 17 is rigidly secured, as best illustrated in Fig.2. The plate 21 has trunnions 23 that are journaled for pivotal movementon a xed axis in brackets 25 of a suitable type that are rigidly affixedto the inside of the longitudinal side frame members 27 of the subframe6. The plate 21 may be employed to carry pumps and valves and otherhydraulic apparatus generally indicated at 29. The axis of the trunnions23 is offset below the axis of the cylinder 17 as readily seen inFig. 1. A piston 31 (Fig. 3) reciprocates within the cylinder 17 as aresult of suitable control by apparatus 29 over the oil pressure in thecylinder. The piston 31 has the usual rod 33 connected thereto andextending out the rear end 35 of the cylinder through a suitable glandand bearing device 37. It is understood that the piston and rod may beintegral or separate parts joined together, this being immaterial in thepractice of the invention.

In accordance with the teachings of this invention, the rod 33 ispivotally connected to the body 7 on a transverse axis which is spacedabove the axis of the cylinder and rod. This may be accomplished bymeans of a fitting 39 that is rigidly secured to the rod end and whichhas bearing surfaces therein that are adapted to receive a trunnion 41extending between legs or brackets 43 that are aflixed to the bottom ofthe body 7. When the body is in lowered position, the piston 31 isadjacent the base 19 of the cylinder 17 as shown in full lines 1n Fig.3. When rice the body is in elevated position, as the result of theapplication of oil pressure to the front radial face of the piston 31,the piston 31 will approach the rear end 35 of the cylinder 17 as shownin dotted lines in Fig. 3 (and also in Fig. 4). It will be appreciatedthat the dotted line positions shown in Fig. 3 is schematic since, inthe elevated position, the cylinder and piston and rod unit will bepivoted upwardly from the horizontal position about the fixed trunnionaxis 23.

In the direct acting hoist of Figs. l-3, the external forces acting onthe cylinder and rod lie along the straight lines 100 and 102 connectingthe centers of front trunnion 23 and rear trunnion 41. Preferably, theeccentricity of the axes of the trunnions 23 and 41 is such that theline of force intersects the axis of the rod 33 at a point between thepiston 31 and the bearing device 37. This relationship preferably existsat all angles of body elevation such as illustrated in Fig. 3 whereineach of the lines of force 100 and 102, for the mechanism in lowered andelevated positions, respectively, of the body, intersect the axis of therod 31 at a point between the piston 31 and the gland or bearing device37.

In the embodiment of Fig. 4, the lines of force do not adhere to thepreferred relationship just mentioned, i. e., they do not intersect therod between the piston 31 and gland device 37 at low angles of bodyelevation. This is illustrated by the line of force 104 which intersectsthe rod axis to the rear of the bearing device 37. However, the line offorce for the extended rod position at high angles of body elevation(not shown) does pass through the rod axis at a point between the piston31 and the gland device 37. This relationship of the lines of force tothe rod axes is due to the novel mounting of the cvlinder 17 on theframe which is disclosed and claimed in a copending application of thepresent inventor entitled Floating Cylinder and Link Hoist. Serial No.252,395, filed October 20, 1951. In this hoist construction, the rearend of the cylinder is pivotally supported at 5 upon the interconnectedends of a forwardly extending link 53 and a rearwardly extending link55. The rear end of link 55 is pivoted at 57 to a bracket 59 that isfixed on the sub-frame 6 or chassis 3. The forwardlv extending link 53is pivoted at 60 to a roller or other suitable bearing surface 61 thatis provided on the pivot plate 21 at the base of the cvlinder 17. Thesurface 61 is slidable in a horizontal slot provided bv a bracket 63afiixed on the sub-frame 6. When the body is fullv elevated. the links53 and 55 become in substantial rectilinear alignment with each other.lt will thus be recognized that the line of force at the higher anglesof elevation approaches the line between the center of pivot 41 and thecenter of the pivot 60 at the forward end of the link 53, and thereforeintersects the rod axis between the piston 31 and the bearing device 37.

It is evident from Fig. l that the unward offset of trunnion 41 from theaxis of the rod 33 increases the moment arm of the force applied bv thehvdraulic unit to the body 7. This is the case because the perpendiculardistance or moment arm between a line of force passing through the axisof trunnion 41 and the axis of the bodv pivot 11 is greater than themoment arm about the trunnion 11 of a line of force passing through apoint on the axis of the rod 33 which corresponds to the axis 41.

Another advantage of the oset or eccentric relationship between bodv androd pivot 41 is the pre-existing effect that this is known to have onthe stress in the rod 33. Maximum bending of the rod occurs at this endas a result of this tvpe of connection. However, in the conventionalconnection. such as illustrated in Fig. 5 wherein the trunnion 41 lieson the axis of the rod 33, unpredictable manufacturing variations. playbetween the stationary and moving parts, and friction on the trunnion 41are likelv to induce eccentricity so that the rod 33 behaves as anunstable column. It is not uncommon for this to result in rod failuresdue to the fact that the effect of these factors could not be adequatelyconsidered in the stress analvsis of the rod. In the present design.this possibility is eliminated by the eccentric construction.

In conventional constructions, it is also common for binding or cockingof the piston and rod. with respect to their respective bearing surfacesin cylinder 17 and bearing and gland device 37. to ocur as indicated inFig. 5. This causes the axis ofthe rod 33 to assume an angle relative tothe axis of the cylinder 17 and concentrates the vertical components offorce on the rod on the small areas of contact between the piston andcylinder and the rod and gland device 37. This increases the rate ofwear of the unit 15 so that leakage is likely to occur after arelatively short period of usage. In the present preferred constructionwherein the line of force intersects the rod axis between the gland 37and the piston 31, these harmful effects are eliminated. In the regionswherein the line of force has this relationship to the rod axes, itsvertical reaction components between the piston 3l and the cylinder 17and between the rod 33 and the bearing device 37 are both in the samedirection. In other words, the transverse force is applied to the rodand piston at a point located between the two points of support ratherthan outside the two points of support so that the rod and piston areloaded like a simple beam rather than like a cantilever beam. Thetendency then is to displace the axis of the rod 33 parallel to the axisof the cylinder. The side reaction loads are therefore distributed oversubstantially the full possible areas of contact between the piston andthe cylinder 17 and the rod and the gland 37. The unit stress istherefore reduced to a minimum as are the friction forces. The magnitudeof the side loads on the cylinder and on the gland device 37 isinversely proportional to the distance or overlap between the piston andthe rear end 35 of the cylinder. Hence, their harmful effect at lowangles of elevation wherein the piston 31 is remote from the end 35 isless than at higher angles of elevation wherein the piston 31 approachesthe rear end of the cylinder. Thus, substantial improvement may still beobtained in constructions, such as that of Fig. 4, wherein the desiredpath of the line of force is not obtained at the lower angles ofelevation.

As already indicated, it is preferred that the connections between thecylinder and frame, and between the rod and the body, be both offset onopposite sides of the axis of the unit 15. However, certain benefits ofthe invention may still be obtained if the base 19 of the cylinder ispivoted to the frame on an axis which lies on its axis as illustrated at23 in the conventional unit 15' of Fig. 5. It is also evident that theconnections between the cylinder and rod and the body and frame could bereversed within the scope of the invention. In this case, the unit 15 ofFig. 3 would be simply rotated 180 degrees about an axis normal to theplan of the drawing so that the base 19 would be pivoted to the body onan axis which is offset upwardly from the axis of the cylinder and therod 33 pivoted to the sub-frame 6 on an axis which is spaced below theaxis of the rod and cylinder.

Other modifications will appear to those in the art, hence, it is notintended to limit the invention to the specific constructions that havebeen shown herein for the purpose of illustration.

What is claimed is:

l. Hoist apparatus for tilting a body with respect to a frame on whichit is mounted, comprising, in combination, a pressure cylinder memberhaving an aperture at one end with a bearing surface in said aperture, apiston in the cylinder, a rod member connected to the piston andextending through the aperture, a movable connection between one of themembers and the frame, means for operatively connecting the other memberto the body, and an operative connection between the other member andsaid means, a straight line through said connections intersecting theaxis of the members at the higher angles of body elevation at a pointbetween the piston and the bearing surface.

2. Hoist apparatus for tilting a body member with respect to a framemember on which it is mounted, comprising, in combination, a pressurecylinder having au aperture at one end with a bearing surface therein, apiston in the cylinder, a rod connected to the piston and extendingthrough said aperture and supported on said bearing surface, and meanswhereby said cylinder and rod are operatively connected to different ofsaid memhers on axes that are transverse to the longitudinal axis of therod and offset from said rod axis on opposite sides thereof in thedirection of the respective members to which the cylinder and rod areconnected. said means including portions extending from the axes to saidcylinder and rod and making fixed angles with respect to the axis of thecylinder and rod, said offset axes being located so that the line offorce on the rod intersects the longitudinal rod axis at a point betweenthe bearing surface and the piston whereby the transverse load components on the piston and rod act in the same directlon.

3. Hoist apparatus for tilting a body with respect to a frame on whichit is mounted, comprising, in combination, a pressure cylinder pivotallyconnected to the fram: so as to be located beneath the body, a piston inthe cylinder, a rod secured to the piston and extending out of one endof the cylinder, means making a fixed angle with the rod and pivotallyconnecting the rod to the body, the cylinder and rod pivotal connectionsbeing located on opposite sides of the rod axis with the rod pivotalconnection spaced between it and the body and located so that thetransverse loads on the piston and rod due to the force applied by therod to the body act in the same direction.

4. A device for separating a pair of relatively movable memberscomprising a pressure cylinder, a piston in the cylinder, a rod securedto the piston and extending out of one end of the cylinder, saidcylinder being pivoted to one member and said rod being pivoted to theother on axes offset on opposite sides of the axis of the rod and spacedfixed distances from said axis, the line of centers of said rod andcylinder pivots intersecting the axis of the cylinder and rodintermediate their ends.

5. Pressure actuated means comprising a hlousing member and a piston androd member operably disposed within the housing member and extendingthrough one end thereof, means adjacent the other end of housing memberfor a force transmitting connection, means adjacent the free end of thepiston and rod member for a force transmitting connection, saidconnections beinglaterally offset on opposite sides of the axis of themembers and spaced fixed distances from said axis.

6. A pressure actuated body moving device comprising a housing memberhaving a bearing at one end, a piston and rod member operably disposedwithin the housing and extending through the bearing to the exterior ofthe housing, connecting means adjacent the end of the housing memberopposite the bearing, connecting means adjacent the end of the rodmember, both said connecting means extending transversely to theirrespective members and making xed angles with respect to the axis of themembers, said connecting means having a line of centers which intersectsthe axis of the members at points between the piston and bearingthroughout a substantial part of the range of relative movement of themembers.

7. Hoist apparatus for tilting a body member with respect to a framemember on which it is mounted comprising, in combination, a pressurecylinder having an aperture at one end, a piston in the cylinder, a rodconnected to the piston and extending through said aperture, an armsecured to said rod to extend transversely thereof at a fixed angle,said cylinder being operatively connected to one of the members on atransverse axis spaced transversely from the centerline of the cylinderand rod and on the opposite side of said centerline from said arm, saidarm being operatively connected to the other of the members on atransverse axis between the rod axis and the member, said cylinder,piston and rod being located beneath the body member.

References Cited in the file of this patent UNITED STATES PATENTS

